This invention relates to twist-on wire connectors used in electrical systems; and, more particularly to a compact electrical connection system for twisted wires and having an electrically insulating shell.
There is a continuing need to conveniently connect electrical wires together in an electrical system. The most common type connector, and the one extensively used by electrical contractors and do-it-yourselfers is the “twist-on connector.” This connector is also commonly referred to as a wire nut, a cone connector, or a thimble connector.
The connector typically has an insulated plastic shell molded over a sharpened spring steel inner coil and is used to fasten together two or more electrical conductors. Regarding their use, electricians tend to prefer to twist electrical wires together and use an electrical tape to insulate the connection. This has the advantage of an electrician seeing that the wires are indeed twisted together and have achieved a good mechanical connection. Indeed, a practice used by many electricians who use a twist-on connector is to pre-twist the wires before using the connector so to ensure that the wires are indeed twisted together before applying the connector, this regardless of manufacturer instructions.
Twist-on wire connectors are available in a variety of sizes and shapes. While their exterior covering is typically an insulating plastic, their means of connection is a tapered metal coil insert, which threads onto the wires and holds them securely. When such a connector is twisted onto the stripped and twisted-together ends of wires, the wires are drawn into the connector's metal insert and squeezed together inside it. Electrical continuity is maintained by both the direct twisted wire-to-wire contact and by contact with the metal insert. Additionally, the threads cut into the wires by the tapered metal insert are what hold the twist-on wire connector onto the assembly.
Twist-on wire connectors are typically installed by hand and may have external grooves to make them easier to handle and apply. Wing-like extensions are commonly molded into higher quality connectors to reduce an installer's muscle fatigue when installing large numbers of connectors. Additional tools such as a common nut driver are also used to help reduce installer fatigue during the installation of a large numbers of such connectors. The connectors are commonly color-coded to indicate connector size and, hence, their capacity. They are commonly used as an alternative to terminal blocks or the soldering together of conductors since they are quicker to install and, unlike soldered connections, allow easy subsequent removal for future modifications. Twist-on connectors are not often used on wire gauges thicker than AWG #10 (5.26 mm2), because these wires are too stiff to be reliably connected using this method. Instead, set screw connectors, clamps, or crimp connectors are used in these instances.
There are some specialized versions of twist-on connectors. Ceramic twist-on connectors, for example, are made for high-temperature applications, such as heating appliances. Ordinary twist-on connectors are not rated for wet use (such as outdoor exposure outdoors or underground burial). Special, gel-filled connectors are used in this circumstance.
Twist-on wire connectors are not generally recommended for use with aluminum wire. The US Consumer Product Safety Commission does not approve their use with aluminum wire, and approves only two (alternative) methods of connection. Despite this, several companies manufacture twist-on connectors which they claim are designed specifically for, and rated for, use with aluminum conductors.
Special feed through twist-on wire connectors differ from standard wire connectors in that they have an additional opening at the top of the insulated cap. This allows a single-conductor bare wire to be pushed through the hole, forming a “pigtail” section which is attached to a grounding screw. These feed-through connectors are commonly referred to as “screw-on grounding connectors.” For some applications, the pigtail may be unterminated, or it may end in a pre-installed spade lug. One version (colored white) is used, for example, for splicing neutral wires in a device box, while leaving the pigtail free for connection to a receptacle, for example. Another version (colored green) is used as a grounding pigtail and is similar to the feed through twist-on wire connector previously described.
As noted above, previous twist-on connectors are comprised of a tapered coiled metal insert surrounded by an insulating material which ranges from plastic to polymers to rubber. Typically, innovation regarding twist-on connectors relates to material changes; however, the fundamental of a coil inside an insulator is basic to all of these current connector constructions. As an example, adding gels for waterproofing is a recent innovation, but the fundamental structure of a twist-on connector is the same as in earlier constructions.
The most expensive part of a basic twist-on connector is the tapered coil itself and its manufacture. The sole purpose of the coil is to twist the wires together, but in doing so, it adds to the bulkiness of the connector. Since it is the practice of electricians to pre-twist the wires anyway (again, so that they can visually see they have a good, twisted, mechanical bond), the role of the tapered coil is essentially obsolete.